Phagocytosis of Candida albicans by human leukocytes: opsonic requirements

The kinetics of phagocytosis of Candida albicans by human polymorphonuclear leukocytes was studied. The basis for these studies was a phagocytic assay with use of C. albicans radiolabeled with [3H]adenine. After incubation of leukocytes with C. albicans, extracellular C. albicans was separated from phagocytes by centrifugation through Ficoll-Hypaque suspensions (specific density, 1.175 g/cm3). Recovery of leukocytes by this technique was greater than or equal to 85%. The initial rate of phagocytosis was more rapid than that previously reported for bacteria. Ethylenediaminetetraacetate, vinblastine, ethylmaleimide, NaF, and ice bath temperature completely inhibited phagocytosis. Colchicine had no effect, and NaN3 was partially inhibitory. Pooled sera possessed low titers (greater than or equal to 1:40) of heat-stable opsonins. The opsonic activity of pooled sera was shown to depend primarily upon complement activated through both the alternative and classical pathways. Decomplemented hyperimmune sera were opsonic at high dilutions (greater than or equal to 1:160), and complement amplified the initial rate of ingestion seen with hyperimmune sera.